The ongoing difficulty of accurately measuring the Earth’s ocean heat content has led to premature “skeptic” claims about ocean cooling. A recent paper Von Schuckmann & Le Traon (2011) put the kibosh on ocean cooling claims. They find that from 2005 to 2010 the global oceans (10 to 1500 metres down) have continued to warm, although they caution that their result is based on the assumption that there are no more systematic errors in the data gathered from ARGO floats which measure ocean heat.

The more (data), the merrier

The ARGO float network began rollout in 2000, but prior to 2005 there wasn’t sufficent global coverage, and because of this Von Schuckmann and Le Traon (2011) start their analysis from 2005 onwards. The authors found that only after November 2007 (when ARGO was 100% complete) is the ARGO network sufficiently robust to give accurate short-term trends of what they term ‘global ocean indicators’. This being steric sea level changes (sea level rise from thermal expansion as the oceans warm), heat content, and ocean salinity. This is probably best illustrated in the figure below, where the authors apply their method of analysis to the satellite sea surface height (SSH) data (AVISO):

Figure 2 -Method validation using gridded altimeter SSH measurements (AVISO): gridded SSH during 2005–2010 has been subsampled to the Argo proﬁle position and the simple box averaging method has been applied. Global mean SSH derived from the AVISO grid (bold line) is compared to its corresponding subsampled result.

The two lines represent the satellite data and a subsampled set using the position of the ARGO float profiles and the authors ‘box averaging’ method – a method to account for the irregular distribution of ARGO floats in the ocean, and missing and spurious (faulty) data. After 2007 (vertical dashed line), when the ARGO installation is complete, it is obvious that both sets show greater agreement. This highlights how sensitive the short-term trends are to the number of ARGO floats in the network.

Errors reduce as the length of observation increases

Von Schuckmann & Le Traon (2011) also estimate the errors in global trends from the period analysed, and also future error uncertainty. For the 2005-2010 period the error uncertainty is plus/minus 0.1 watt per square metre; quite large considering the global trend over the period is 0.55 watts per square metre. However, after 15 years of observations the uncertainty drops considerably, down to ± 0.02 watts per square metre. This demonstrates how longer periods of observation, along with the complete ARGO network, are critical to derive more accurate long-term ocean trends.

Conclusion

The ARGO network was completed in November 2007, and only since then has the network been able to provide more robust short-term trends. Over the period 2005-2010 the oceans (10-1500 meters down) have warmed 0.55 watts per square meter, but error uncertainty is almost 20%. Uncertainty will reduce as the length of the observational record increases, but Von Schuckmann and Le Traon (2011), caution that this is provided no more systematic errors remain in the network.

[S]ince 1950, the planet released about 20 percent of the warming influence of heat-trapping greenhouse gases to outer space as infrared energy. Volcanic emissions lingering in the stratosphere offset about 20 percent of the heating by bouncing solar radiation back to space before it reached the surface. Cooling from the lower-atmosphere aerosols produced by humans balanced 50 percent of the heating. Only the remaining 10 percent of greenhouse-gas warming actually went into heating the Earth, and almost all of it went into the ocean.

Note that this Journal of Geophysical Research-Atmospheres study was done “without using global climate models.”

Below are old comments from the earlier Facebook commenting system:

Bru makes an excellent point about the thermal momentum of the Earth System. This is yet another of those critically important details that lies far outside the “normal” range of units and size that people are accustomed to dealing with. (Like parts per million or billion, degrees of warming per century, billions of tons of Greenland ice lost per year, etc.)

The other big issue in this vein is the long atmospheric lifetime of CO2. Many people are under the impression that global warming is just like other forms of pollution, meaning if we cut our CO2 emissions by, say, 50%, we’d see a 50% reduction in warming within a few months or a couple of years. CO2’s long lifetime plus the momentum of all that heat in the ocean add up a very long cool down time, even if we’re incredibly aggressive in cutting our emissions.

A modest issue on precision of phrasing. You write “Over the period 2005-2010 the oceans (10-1500 meters down) have warmed 0.55 watts per square meter”.

“have warmed” tends to imply a total change from 2005 to 2010, which would be some number of Joules (energy) per square meter. One might more precisely say “Over the period 2005-2010 the oceans (10-1500 meters down) warmed at a rate of 0.55 watts (Joules per second) per square meter.”

I confess when I first read “have warmed 0.55 watts per square meter” my reaction was severe disbelief, because the units after 0.55 were physically impossible relative to the English grammar.

Is weather becoming more extreme?
big picture, boston.
Extreme weather events have always been with us, and always will be. One can’t point to a single severe storm, or even an entire harsh winter, as evidence of climate change. But a trend of weather intensity, and oddity, grows. Droughts linger longer. Hurricanes hit harder. Snowstorms strike lon…

The last graph is interesting: I’m sure I saw somewhere else that 90% of the extra energy is going into the ocean. This picture makes it look like a much higher fraction. A nitpick: “Clearly much heat is finding it’s way down”: should be “..its…”.